1. Field of the Invention
The present invention relates to a Cathode Ray Tube (CRT), and in particular, to a shape of a cone for a CRT having a deflection unit.
2. Description of Related Art
A CRT is an electronic tube which deflects electron beams emitted from an electron gun to a phosphor screen in the horizontal and vertical directions, and lands those electron beams on that screen, thereby striking the phosphors and displaying the desired images. The deflection of the electron beams is effected by a deflection unit, which is mounted around the outer circumference of a funnel (practically, the outer circumference of a cone forming the vacuum tube), and generates horizontal and vertical magnetic fields.
The CRT has been mainly used in color televisions and computer monitors, and have recently been used for a high-grade product, such as an HDTV.
In order to improve the definition of the CRT, that is, in order use the CRT for HDTV or other OA equipment, or to enhance the brightness of the CRT, the deflection frequency of the deflection yoke must be increased, which results in the deflection power being elevated so that the leakage of magnetic fields and the power consumption are increased.
Such a problem made due to the elevation of the deflection power is a critical factor in improving the definition of the CRT.
In this connection, a technique of enhancing the deflection efficiency of the deflection yoke for the electron beams by reducing the diameter of a neck of the vacuum tube and the neck-sided outer diameter of the funnel is conventionally used in manufacturing the CRT. However, with the technique, a so-called Beam Strike Neck (BSN) phenomenon occurs where the electron beams to be directed toward the corners of the screen collide against the neck-sided inner wall of the funnel, and the desired image is not obtained.
As the trajectories of the electron beams have not conventionally measured in a suitable manner, the manufacturing of the CRT depends largely upon the occasional experiences of the manufacturer or through trial and error. In this situation, it becomes difficult to effectively solve the BSN problem of the electron beams.
The technique of lowering the deflection power simply to maximize the deflection efficiency by reducing the neck-sided outer diameter of the funnel is limited due to the BSN problem of the electron beams.
Accordingly, efforts have been made to appropriately form the cone of the funnel mounted with the deflection unit in CRTs (such that the section thereof vertical to the tube axis is rectangular-shaped), and solve the BSN problem of the electron beams while lowering the deflection power.
That is, the shape of the cone is improved such that the deflection unit for forming a deflection magnetic field comes closer to the scanning trajectories of the electron beams, thereby reducing the deflecting sensitivity and lowering the power consumption.
With the CRT having a rectangular-shaped cone, the inner and outer surfaces of the cone are convex to the outside of the tube axis of the CRT. When a deflection unit is mounted around the rectangular-shaped cone, the shape of the cone becomes to be a factor of preventing the electron beams from coming closer to the scanning trajectories of the electron beams. This is because the cone is simply formed with a rectangular section without considering the BSN margin of the electron beams in the horizontal, the vertical and the diagonal directions of the electron beams scanned toward the phosphor screen from the electron gun.
Accordingly, with a CRT having such a rectangular-shaped cone, the shape of the cone causes a problem in minimizing the deflection power.